(1) Field of the Invention
The present invention relates to transflective liquid crystal display devices, more particularly, to an art which is effective in applying the transflective liquid crystal display device to an IPS (In Plane Switching) mode.
(2) Description of the Related Art
A transflective liquid crystal display device which has a transmissive unit and a reflective unit in one sub-pixel is used as a display for portable devices.
The transflective liquid crystal display device employs a vertical electric field system in which electric field is impressed to a liquid crystal interposed between a pair of substrates, in the direction perpendicular to the substrate plane of the pair of substrates, thereby driving the liquid crystal. In this case, in order to match the property of the transmissive unit to the property of the reflective unit, a level difference is prepared between the transmissive unit and the reflective unit, and furthermore a retardation film is prepared between a polarizing plate and the liquid crystal layer.
On the other hand, as one of liquid crystal display devices, an in-plane-switching (IPS)-mode liquid crystal display device is well known. In the IPS-mode liquid crystal display device, a pixel electrode (PIX) and an opposed electrode (CT) are formed on the same substrate, and electric field is impressed between the electrodes to rotate the liquid crystal in the substrate plane, thereby performing light and dark control. Therefore, there is a feature that the lightness and darkness of a display image is not reversed even when the screen is seen from at an oblique angle. In order to efficiently use this feature, composing a transflective liquid crystal display device by employing the IPS-mode liquid crystal display device is proposed, for example, by Japanese Patent Application Laid-Open Publication No. 2003-344837 and Japanese Patent Application Laid-Open Publication No. 2005-338256.
As a method of composing the transflective liquid crystal display device with the IPS mode, in Japanese Patent Application Laid-Open Publication No. 2003-344837, a half-wave plate is prepared in a transmissive area and a reflective area, and the transmissive area is driven by a lateral electric field and the reflective area is driven by a vertical electric field. On the other hand, in Japanese Patent Application Laid-Open Publication No. 2005-338256, a half-wave plate is prepared only in the reflective area, and the transmissive area and the reflective area are both driven by a lateral electric field.